Causes and consequences of increased sympathetic activity in renal disease

Association of E/E' and NT-proBNP with renal function in patients with essential hypertension

Objectives

To evaluate the association of left ventricular (LV) diastolic function and N-terminal pro-brain natriuretic peptide (NT-proBNP) with renal function in essential hypertension.

Methods

LV diastolic function was estimated by the ratio of early diastolic velocities (E) from transmitral inflow to early diastolic velocities (E′) of tissue Doppler at mitral annulus (septal corner); NT-proBNP was measured in 207 hypertensive patients (mean age 56±14 years). The subjects were classified into 3 groups: E/E′≤10 group (n = 48), 10<E/E′≤15 group (n = 109) and E/E′>15 group (n = 50). The renal function was estimated by glomerular filtration rate (GFR) with ^99mTc-DTPA. GFR from 30 to 59 ml/min/1.73 m² was defined as Stage 3 chronic kidney disease (CKD). GFR was also estimated using the modified MDRD equation. Albuminuria was defined by urinary albumin/creatinine ratio (UACR).

Results

GFR was lower and UACR was higher in E/E′ >15 group than in 10< E/E′ ≤15 group or E/E′ ≤10 group (p<0.0001), GFR was significantly negative and UACR was positive correlated with E/E′ and NT-proBNP (p<0.0001). In multivariate stepwise linear analysis, GFR had significant correlation with age (p = 0.001), gender (p = 0.003), E/E′ (p = 0.03), lgNT-proBNP (p = 0.001) and lgUACR (p = 0.01), while eGFR had no significant correlation with E/E′ or lgNT-proBNP. Multivariate logistic regression analysis, adjusted for potential confounding factors, showed that participants in E/E′>15 group were more likely to have Stage 3 CKD compared with those in E/E′≤10 group with an adjusted odds ratio of 8.31 (p = 0.0036).

Conclusions

LV diastolic function, assessed with E/E′ and NT-proBNP is associated with renal function in essential hypertension.

Heart rate variability in peritoneal dialysis patients: what is the role of residual renal function?

BACKGROUND

The relationship between heart rate variability (HRV) and residual renal function (RRF) has not been elucidated previously.

METHODS

In this cross-sectional study, HRV was evaluated in 71 peritoneal dialysis patients. Patients were divided into RRF decline group, RRF stable group and anuric group.

RESULTS

RRF was negatively correlated with SDNN (r = -0.284, p = 0.017), TP (r = -0.247, p = 0.039), and HF (r = -0.238, p = 0.047). Significant sympathetic nerve activation was found in the RRF decline group (significantly lower SDNN, SDSD, RMSSD, pNN50, LF, HF, TP and higher LF/HF ratio) as compared to the RRF stable and anuric groups. Besides, significantly parasympathetic activation was found in the anuric group (the lowest LF/HF ratio as compared to the other groups (both p < 0.05). Multivariate stepwise regression analysis showed that the status of RRF was an independent factor associated with HRV parameters.

CONCLUSION

This study showed autonomic nervous function in peritoneal dialysis patients was associated with a different status of RRF.

Cardiovascular risk in chronic kidney disease: role of the sympathetic nervous system

Patients with chronic kidney disease are at significantly increased risk for cardiovascular disease and sudden cardiac death. One mechanism underlying increased cardiovascular risk in patients with renal failure includes overactivation of the sympathetic nervous system (SNS). Multiple human and animal studies have shown that central sympathetic outflow is chronically elevated in patients with both end-stage renal disease (ESRD) and chronic kidney disease (CKD). SNS overactivation, in turn, increases the risk of cardiovascular disease and sudden death by increasing arterial blood pressure, arrythmogenicity, left ventricular hypertrophy, and coronary vasoconstriction and contributes to the progression renal disease. This paper will examine the evidence for SNS overactivation in renal failure from both human and experimental studies and discuss mechanisms of SNS overactivity in CKD and therapeutic implications.

Cardioprotective effect of renalase in 5/6 nephrectomized rats

Cardiovascular disease (CVD) remains one of the most common causes of morbidity and mortality in patients with chronic renal disease. It has been recently postulated that the loss or reduced levels of renalase in patients with chronic renal disease are, at least in part, responsible for elevated plasma catecholamine levels, which leads to increased CVD. Therefore, the aim of the present study was to evaluate whether renalase administration might serve as a therapeutic drug, decreasing the severity of CVD in 5/6 nephrectomized (Nx) rats. The current study was conducted on 30 male Wistar albino rats divided into the following groups: group I: sham-operated rats that received phosphate-buffered saline (PBS) subcutaneously (s.c.) for 4 weeks following sham operation, group II: rats in which 5/6 Nx was done and then the rats received PBS daily s.c. for 4 weeks following 5/6 Nx, and group III: rats in which 5/6 Nx was done and then the rats received recombinant renalase daily s.c. for 4 weeks following 5/6 Nx. 5/6 nephrectomy resulted in a significant increase in mean arterial pressure, left ventricular (LV)/body weight ratio, LV hydroxyproline concentration, plasma creatinine, blood urea nitrogen (BUN), and noradrenaline (NA) levels as well as significant decrease in LV papillary muscle developed tension in group II compared with the sham-operated group I. Administration of renalase to group III resulted in significant amelioration of all studied parameters with the exception of plasma creatinine and BUN which were not significantly different from nontreated group II. The results of the current study identify renalase as a new therapeutic modality that might modulate cardiac function and systemic blood pressure in renalase-deficient states like chronic renal disease.

Evidence and consequences of the central role of the kidneys in the pathophysiology of sympathetic hyperactivity

Chronic elevation of the sympathetic nervous system has been identified as a major contributor to the complex pathophysiology of hypertension, states of volume overload – such as heart failure – and progressive kidney disease. It is also a strong determinant for clinical outcome. This review focuses on the central role of the kidneys in the pathogenesis of sympathetic hyperactivity. As a consequence, renal denervation may be an attractive option to treat sympathetic hyperactivity. The review will also focus on first results and the still remaining questions of this new treatment option.

Cardio-renal syndrome: an entity cardiologists and nephrologists should be dealing with collegially

Heart failure may lead to acute kidney injury and vice versa. Chronic kidney disease may affect the clinical outcome in terms of cardiovascular morbidity and mortality while chronic heart failure may cause CKD. All these disorders contribute to the composite definition of cardio-renal syndromes. Renal impairment in HF patients has been increasingly recognized as an independent risk factor for morbidity and mortality; however, the most important clinical trials in HF tend to exclude patients with significant renal dysfunction. The mechanisms whereby renal insufficiency worsens the outcome in HF are not known, and several pathways could contribute to the "vicious heart/kidney circle." Traditionally, renal impairment has been attributed to the renal hypoperfusion due to reduced cardiac output and decreased systemic pressure. The hypovolemia leads to sympathetic activity, increased renin-angiotensin-aldosterone pathways and arginine-vasopressin release. All these mechanisms cause fluid and sodium retention, peripheral vasoconstriction and an increased congestion as well as cardiac workload. Therapy addressed to improve renal dysfunction, reduce neurohormonal activation and ameliorate renal blood flow could lead to a reduction in mortality and hospitalization in patients with cardio-renal syndrome.

Sympatho-renal axis in chronic disease

Essential hypertension, insulin resistance, heart failure, congestion, diuretic resistance, and functional renal disease are all characterized by excessive central sympathetic drive. The contribution of the kidney's somatic afferent nerves, as an underlying cause of elevated central sympathetic drive, and the consequences of excessive efferent sympathetic signals to the kidney itself, as well as other organs, identify the renal sympathetic nerves as a uniquely logical therapeutic target for diseases linked by excessive central sympathetic drive. Clinical studies of renal denervation in patients with resistant hypertension using an endovascular radiofrequency ablation methodology have exposed the sympathetic link between these conditions. Renal denervation could be expected to simultaneously affect blood pressure, insulin resistance, sleep disorders, congestion in heart failure, cardiorenal syndrome and diuretic resistance. The striking epidemiologic evidence for coexistence of these disorders suggests common causal pathways. Chronic activation of the sympathetic nervous system has been associated with components of the metabolic syndrome, such as blood pressure elevation, obesity, dyslipidemia, and impaired fasting glucose with hyperinsulinemia. Over 50% of patients with essential hypertension are hyperinsulinemic, regardless of whether they are untreated or in a stable program of treatment. Insulin resistance is related to sympathetic drive via a bidirectional mechanism. In this manuscript, we review the data that suggests that selective impairment of renal somatic afferent and sympathetic efferent nerves in patients with resistant hypertension both reduces markers of central sympathetic drive and favorably impacts diseases linked through central sympathetics-insulin resistance, heart failure, congestion, diuretic resistance, and cardiorenal disorders.

Renal nerves in the maintenance of hypertension: a potential therapeutic target

Renal sympathetic efferent and afferent nerves, which lie within and immediately adjacent to the wall of the renal arteries, contribute to the maintenance of hypertension. Because the causative factors of hypertension change over time, denervation of both efferent and afferent renal nerves should result in long-term attenuation of hypertension. The importance of the renal nerves in hypertensive patients can now be defined with the novel development of percutaneous, minimally invasive renal denervation from within the renal artery using radiofrequency energy as a therapeutic strategy. Studies thus far show that catheter-based renal denervation in patients with resistant essential hypertension lowers systolic blood pressure 27 mm Hg by 12 months, with the estimated glomerular filtration rate remaining stable. The decrease in arterial pressure after renal denervation is associated with decreased peripheral sympathetic nervous system activity, suggesting that the kidney is a source of significant central sympathetic outflow via afferent renal nerve activity.

Podocyte dysfunction in aging--related glomerulosclerosis

We review podocyte molecular structure and function, consider the underlying mechanisms related to podocyte dysfunction and propose that podocyte dysfunction be considered in the evaluation and management of age-associated glomerulosclerosis. With aging, progressive sympathetic activation, increased intrarenal renin-angiotensin system (RAS) activity, endothelin system and oxidative stress and reduced nitric oxide (NO)-availability can damage podocytes. Apoptosis and proliferation are the principal podocyte changes following injury with the latter leading to sclerosis and loss of nephrons. Podocyte loss can be evaluated by either determining their average number in biopsed glomeruli or by estimating podocyte number or their associated molecules in urine sediment. Podocyturia may be considered a marker of active glomerular disease. Preliminary data suggest that antiadrenergic drugs, angiotensin converting enzyme (ACE) inhibitors, RAS blocking drugs, endothelin system inhibitors and reduced oxidative stress can protect podocytes. Thus podocytes appear to play an important role in the pathogenesis, evaluation and therapy of age related glomerulosclerosis.

Renal denervation and hypertension

Essential hypertension remains one of the biggest challenges in medicine with an enormous impact on both individual and society levels. With the exception of relatively rare monogenetic forms of hypertension, there is now general agreement that the condition is multifactorial in nature and hence requires therapeutic approaches targeting several aspects of the underlying pathophysiology. Accordingly, all major guidelines promote a combination of lifestyle interventions and combination pharmacotherapy to reach target blood pressure (BP) levels in order to reduce overall cardiovascular risk in affected patients. Although this approach works for many, it fails in a considerable number of patients for various reasons including drug-intolerance, noncompliance, physician inertia, and others, leaving them at unacceptably high cardiovascular risk. The quest for additional therapeutic approaches to safely and effectively manage hypertension continues and expands to the reappraisal of older concepts such as renal denervation. Based on the robust preclinical and clinical data surrounding the role of renal sympathetic nerves in various aspects of BP control very recent efforts have led to the development of a novel catheter-based approach using radiofrequency (RF) energy to selectively target and disrupt the renal nerves. The available evidence from the limited number of uncontrolled hypertensive patients in whom renal denervation has been performed are auspicious and indicate that the procedure has a favorable safety profile and is associated with a substantial and presumably sustained BP reduction. Although promising, a myriad of questions are far from being conclusively answered and require our concerted research efforts to explore the full potential and possible risks of this approach. Here we briefly review the science surrounding renal denervation, summarize the current data on safety and efficacy of renal nerve ablation, and discuss some of the open questions that need to be addressed in the near future.

Major pathways of the reno-cardiovascular link: the sympathetic and renin-angiotensin systems

Chronic kidney disease is often characterized by enhanced activity of the renin-angiotensin system (RAS) and the sympathetic nervous system. Independent of their effect on blood pressure, these systems also contribute to the pathogenesis of both structural and functional cardiovascular abnormalities and contribute importantly to clinical outcome. There is much evidence that the diseased kidneys are of central importance in the pathogenesis of both abnormalities. Inhibitors of the RAS also reduce sympathetic overactivity. Future research should be aimed at addressing the pathophysiological mechanisms causing the enhanced activities. Given the fact that even a small kidney lesion can cause enhanced activity of the RAS and the sympathetic nervous system, it is likely that these pathophysiological mechanisms are operational in more disease conditions, including essential hypertension, heart failure, and obesity/metabolic syndrome.

Renal sympathetic nervous system hyperactivity in early streptozotocin-induced diabetic kidney disease

AIM

We assessed the role of renal sympathetic nervous system in the deterioration of renal hemodynamic and excretory functions in rats with streptozotocin (STZ)-induced diabetic kidney disease (DKD).

METHODS

Male Sprague-Dawley (SD) rats were induced with diabetes mellitus (DM) using STZ (55 mg/kg, i.p.). The acute studies were conducted on denervated anesthetized rats 7 days after STZ administration. Two sets of experiments were performed: clearance experiments in which six 20-min urine and plasma collections were carried out to measure kidney function parameters, and hemodynamic experiments in which the renal nerves were electrically stimulated and responses in renal vascular resistance (RVR) and renal blood flow (RBF) were recorded.

RESULTS

Renal denervation in STZ-induced diabetic rats produced higher fractional excretion of sodium (FE(Na) ) but lower plasma sodium (P(Na) ), glomerular filtration rate (GFR), and plasma creatinine (P(Cr) ) (all P<0.05 vs. innervated diabetic rats). In innervated diabetic rats, renal nerve stimulation (RNS) caused significant attenuation in the renal vasoconstrictor responses (all P<0.05 vs. innervated control). Renal denervation in diabetic rats significantly blunted these responses (all P<0.05 vs. innervated diabetic rats); however, they were significantly higher (all P<0.05) while compared to denervated control counterparts.

CONCLUSIONS

The data demonstrate an early role for the renal sympathetic innervation in the pathogenesis of DKD. If the kidney is prevented from renal sympathetic nerve action renal functional parameters are markedly improved. The data further suggest an early enhancement in renal sensitivity to intrarenal norepinephrine (NE) upon the removal of renal sympathetic tone in STZ-induced diabetic rats.

Relationships of adrenoceptor polymorphisms with obesity

Obesity, hypertension, and type 2 diabetes are rapidly growing public health problems. Heightened sympathetic nerve activity is a well-established observation in obesity, hypertension, and type 2 diabetes. Human obesity, hypertension, and diabetes have strong genetic as well as environmental determinants. Reduced energy expenditure and resting metabolic rate are predictive of weight gain, and the sympathetic nervous system participates in regulating energy balance through thermogenesis. The thermogenic effects of catecholamines in obesity are mainly mediated via the β2, and β3-adrenergic receptors in humans. Further, β2-adrenoceptors importantly influence vascular reactivity and may regulate blood pressure. β-adrenoceptor polymorphisms have also been associated with adrenoceptor desensitization, increased adiposity, insulin resistance, and enhanced sympathetic nervous activity. Many epidemiological studies have shown strong relationships between adrenoceptor polymorphisms and obesity, but the observations have been discordant. This paper will discuss the current topics involving the influence of the sympathetic nervous system and β2- and β3-adrenoceptor polymorphisms in obesity.

Renalase deficiency aggravates ischemic myocardial damage

Chronic kidney disease (CKD) leads to an 18-fold increase in cardiovascular complications not fully explained by traditional risk factors. Levels of renalase, a recently discovered oxidase that metabolizes catecholamines, are decreased in CKD. Here we show that renalase deficiency in a mouse knockout model causes increased plasma catecholamine levels and hypertension. Plasma blood urea nitrogen, creatinine, and aldosterone were unaffected. However, knockout mice had normal systolic function and mild ventricular hypertrophy but tolerated cardiac ischemia poorly and developed myocardial necrosis threefold more severe than that found in wild-type mice. Treatment with recombinant renalase completely rescued the cardiac phenotype. To gain insight into the mechanisms mediating this cardioprotective effect, we tested if gene deletion affected nitrate and glutathione metabolism, but found no differences between hearts of knockout and wild-type mice. The ratio of oxidized (NAD) to reduced (NADH) nicotinamide adenine dinucleotide in cardiac tissue, however, was significantly decreased in the hearts of renalase knockout mice, as was plasma NADH oxidase activity. In vitro studies confirmed that renalase metabolizes NADH and catecholamines. Thus, renalase plays an important role in cardiovascular pathology and its replacement may reduce cardiac complications in renalase-deficient states such as CKD.

Pathogenesis and therapeutic implications of cardiorenal syndrome

Chronic kidney disease (CKD) is now widely accepted as a risk factor for cardiovascular disease and mortality. Heart failure patients with CKD have a worse prognosis. The heart and kidneys act in tandem to regulate blood pressure, vascular tone, diuresis, natriuresis, intravascular volume homeostasis, peripheral tissue perfusion, and oxygenation. Cardiorenal syndrome is a pathophysiological condition in which combined cardiac and renal dysfunction amplifies the progression of failure of the individual organs, and it has an extremely poor prognosis. The identification of patients and the pathophysiological mechanisms underlying each subtype will help physicians to understand the clinical derangements and provide the rationale for management strategies. The evidence from clinical trials conducted on heart failure patients with significant kidney dysfunction is insufficient because most patients are recruited from populations with relatively well-preserved kidney function. In severe volume-loaded patients who are refractory to diuretics and also have kidney dysfunction, the management of cardiorenal dysfunction is challenging, and effective therapy is lacking. In the absence of definitive clinical trials, treatment decisions must be based on a combination of information regarding the individual patient information and an understanding of the individual treatment options.

A functional polymorphism in renalase (Glu37Asp) is associated with cardiac hypertrophy, dysfunction, and ischemia: data from the heart and soul study

BACKGROUND

Renalase is a soluble enzyme that metabolizes circulating catecholamines. A common missense polymorphism in the flavin-adenine dinucleotide-binding domain of human renalase (Glu37Asp) has recently been described. The association of this polymorphism with cardiac structure, function, and ischemia has not previously been reported.

METHODS

We genotyped the rs2296545 single-nucleotide polymorphism (Glu37Asp) in 590 Caucasian individuals and performed resting and stress echocardiography. Logistic regression was used to examine the associations of the Glu37Asp polymorphism (C allele) with cardiac hypertrophy (LV mass>100 g/m2), systolic dysfunction (LVEF<50%), diastolic dysfunction, poor treadmill exercise capacity (METS<5) and inducible ischemia.

RESULTS

Compared with the 406 participants who had GG or CG genotypes, the 184 participants with the CC genotype had increased odds of left ventricular hypertrophy (OR = 1.43; 95% CI 0.99-2.06), systolic dysfunction (OR = 1.72; 95% CI 1.01-2.94), diastolic dysfunction (OR = 1.75; 95% CI 1.05-2.93), poor exercise capacity (OR = 1.61; 95% CI 1.05-2.47), and inducible ischemia (OR = 1.49, 95% CI 0.99-2.24). The Glu37Asp (CC genotype) caused a 24-fold decrease in affinity for NADH and a 2.3-fold reduction in maximal renalase enzymatic activity.

CONCLUSIONS

A functional missense polymorphism in renalase (Glu37Asp) is associated with cardiac hypertrophy, ventricular dysfunction, poor exercise capacity, and inducible ischemia in persons with stable coronary artery disease. Further studies investigating the therapeutic implications of this polymorphism should be considered.

Cardiorenal syndrome: still not a defined entity

Because of the increasing incidence of cardiac failure and chronic renal failure due to the progressive aging of the population, the extensive application of cardiac interventional techniques, the rising rates of obesity and diabetes mellitus, coexistence of heart failure and renal failure in the same patient are frequent. More than half of subjects with heart failure had renal impairment, and mortality worsened incrementally across the range of renal dysfunctions. In patients with heart failure, renal dysfunction can result from intrinsic renal disease, hemodynamic abnormalities, or their combination. Severe pump failure leads to low cardiac output and hypotension, and neurohormonal activation produces both fluid retention and vasoconstriction. However, the cardiorenal connection is more elaborate than the hemodynamic model alone; effects of the renin-angiotensin system, the balance between nitric oxide and reactive oxygen species, inflammation, anemia and the sympathetic nervous system should be taken into account. The management of cardiorenal patients requires a tailored therapy that prioritizes the preservation of the equilibrium of each individual patient. Intravascular volume, blood pressure, renal hemodynamic, anemia and intrinsic renal disease management are crucial for improving patients' survival. Complications should be foreseen and prevented, looking carefully at basic physical examination, weight and blood pressure monitoring, and blood, urine urea and electrolytes measurement.

The role of renal sympathetic nerves in hypertension: has percutaneous renal denervation refocused attention on their clinical significance?

Renal sympathetic efferent and afferent nerves, which lie within and immediately adjacent to the wall of the renal artery, contribute to the pathogenesis of hypertension. Because the causative factors of hypertension change over time, denervation of both efferent and afferent nerves should result in long-term attenuation of the hypertension. The importance of the renal nerves in patients with hypertension can now be defined with the novel development of percutaneous minimally invasive renal denervation from within the renal artery using radiofrequency energy as a therapeutic strategy. Studies thus far show that catheter-based renal denervation in patients with refractory hypertension lowers systolic blood pressure 27 mm Hg by 12 months with estimated glomerular filtration rate remaining stable. An attenuation of hypertension of this magnitude by catheter-based renal sympathetic denervation in combination with pharmacologic therapy is likely to be valuable in decreasing the risks of stroke, left ventricular hypertrophy, heart failure, and chronic renal failure.

Implantable cardioverter defibrillator therapy in chronic kidney disease: a meta-analysis

AIMS

Recent observational studies have shown that implantable cardioverter defibrillator (ICD) patients with chronic kidney disease (CKD) have increased mortality and therefore the value of device therapy in this group has been questioned. The purpose of this meta-analysis was to systematically analyse the effect of renal dysfunction on mortality of ICD patients.

METHODS AND RESULTS

Pubmed, Cochrane clinical trials database, and EMBASE were searched until December 2008. In addition, a manual search was performed using review articles, reference lists of papers, and abstracts from conference reports. Of the 90 initially identified studies, 11 observational studies with 3010 patients were analysed. The meta-analysis of these studies showed that CKD was associated with higher mortality risk (HR = 3.44, 95% CI 2.82-4.21, Z = 12.09, P < 0.001) while there were no significant differences between individual trials (P = 0.09, I(2) = 37.8%). A subgroup analysis which included the four studies that used estimated glomerular filtration rate (GFR) <60 mL/min/1.73 m(2) to define CKD showed a higher mortality in the CKD group as well (HR = 3.06, 95% CI 2.31-4.04, Z = 7.84, P < 0.001) without significant heterogeneity (P = 0.38, I(2) = 5.2%).

CONCLUSION

Our meta-analysis suggests that CKD is associated with increased mortality in patients who receive ICD therapy. Undoubtedly, prospective studies are needed in order to elucidate the impact of different stages of CKD in this setting. Given that the CKD prevalence is rapidly increasing, there is an imperative need for better risk stratification of ICD therapy candidates.

Is kidney ischemia the central mechanism in parallel activation of the renin and sympathetic system?

In chronic kidney disease simultaneous activation of the renin-angiotensin and sympathetic systems occurs. Kidney ischemia seems to play a key role in the pathogenesis. This review firstly summarizes experimental and clinical evidence in chronic kidney disease supporting this idea and addresses the possibility that this mechanism is also relevant in some other disease conditions.

Regulation of blood pressure and cardiovascular function by renalase

The renalase pathway is a previously unrecognized mechanism for regulating cardiac function and blood pressure. In this pathway, renalase, a novel secreted amine oxidase that is inactive at baseline, is rapidly turned on ( ~ 10 fold increase) by either a modest increase in blood pressure or by brief surges in plasma catecholamines. The active enzyme degrades circulating catecholamines, causing a significant fall in blood pressure. Plasma catecholamines not only activate renalase enzymatic activity but also lead to a 3-4 fold stimulation of renalase secretion. The renalase knockout mouse (KO) is hypertensive and exquisitely sensitive to cardiac ischemia. Abnormalities in the renalase pathway are present in animal models of chronic kidney disease (CKD) and hypertension. Two single-nucleotide polymorphisms (SNPs) in the renalase gene were found to be associated with essential hypertension in man. Blood renalase levels are inversely correlated with glomerular filtration rate (GFR) and are markedly reduced in patients with end-stage kidney disease (ESRD). We hypothesize that renalase is secreted into blood by the kidney (although also expressed in heart, skeletal muscle, and small intestine) and plays a key role in regulating blood pressure and cardiovascular function, and that abnormalities in the renalase pathway contribute to the heightened cardiovascular risks observed in patients with CKD.

[Effect of pentoxifylline on the evolution of diabetic nephropathy]

BACKGROUND AND OBJECTIVE

Diabetic nephropathy (DN) is the principal cause of end-chronic kidney disease. Metabolic and hemodynamic components are directly involved. However, convincing data have shown that inflammation participates in the diabetic complications. The aim of this study was to investigate whether the inhibition of the inflammation and pro-inflammatory cytokines with pentoxifylline (PXF) attenuate the progression of the DN.

SUBJECTS AND METHOD

In a prospective, randomized, double-blind, placebo- controlled study, we evaluated the effect of PXF (1200 mg daily) during 12 months, in 34 patients with incipient or established DN. Evaluated parameters were inflammation, pro-inflammatory cytokines and urinary albumin excretion (UAE).

RESULTS

PXF treatment had a reno-protective effect determined by a significant reduction in the UAE in both incipient and established (p<0,01) DN patient. This effect was attributed to a reduction in the C-reactive protein, interleukin-6, tumor necrosis factor-alpha and leptin serum levels (p<0,01).

CONCLUSIONS

PXF treatment caused regression and prevented the progression of renal damage. Thus, PXF should be used in the preventive treatment of DN. These results showed that inflammation and pro-inflammatory cytokines are related to the progression of diabetic nephropathy.

Catheter-based renal sympathetic denervation for resistant hypertension: a multicentre safety and proof-of-principle cohort study

BACKGROUND

Renal sympathetic hyperactivity is associated with hypertension and its progression, chronic kidney disease, and heart failure. We did a proof-of-principle trial of therapeutic renal sympathetic denervation in patients with resistant hypertension (ie, systolic blood pressure >/=160 mm Hg on three or more antihypertensive medications, including a diuretic) to assess safety and blood-pressure reduction effectiveness.

METHODS

We enrolled 50 patients at five Australian and European centres; 5 patients were excluded for anatomical reasons (mainly on the basis of dual renal artery systems). Patients received percutaneous radiofrequency catheter-based treatment between June, 2007, and November, 2008, with subsequent follow-up to 1 year. We assessed the effectiveness of renal sympathetic denervation with renal noradrenaline spillover in a subgroup of patients. Primary endpoints were office blood pressure and safety data before and at 1, 3, 6, 9, and 12 months after procedure. Renal angiography was done before, immediately after, and 14-30 days after procedure, and magnetic resonance angiogram 6 months after procedure. We assessed blood-pressure lowering effectiveness by repeated measures ANOVA. This study is registered in Australia and Europe with ClinicalTrials.gov, numbers NCT 00483808 and NCT 00664638.

FINDINGS

In treated patients, baseline mean office blood pressure was 177/101 mm Hg (SD 20/15), (mean 4.7 antihypertensive medications); estimated glomerular filtration rate was 81 mL/min/1.73m(2) (SD 23); and mean reduction in renal noradrenaline spillover was 47% (95% CI 28-65%). Office blood pressures after procedure were reduced by -14/-10, -21/-10, -22/-11, -24/-11, and -27/-17 mm Hg at 1, 3, 6, 9, and 12 months, respectively. In the five non-treated patients, mean rise in office blood pressure was +3/-2, +2/+3, +14/+9, and +26/+17 mm Hg at 1, 3, 6, and 9 months, respectively. One intraprocedural renal artery dissection occurred before radiofrequency energy delivery, without further sequelae. There were no other renovascular complications.

INTERPRETATION

Catheter-based renal denervation causes substantial and sustained blood-pressure reduction, without serious adverse events, in patients with resistant hypertension. Prospective randomised clinical trials are needed to investigate the usefulness of this procedure in the management of this condition.

Decreased renal function as an independent predictor of re-hospitalization for congestive heart failure

BACKGROUND

Patients with congestive heart failure (CHF) are often re-hospitalized, worsening both their quality of life and prognosis. Although renal dysfunction reportedly increases the risk of CHF, the association between renal dysfunction and re-hospitalization for CHF remains unclear.

METHODS AND RESULTS

Patients with CHF and decreased renal function were reviewed. The estimated glomerular filtration rate (GFR) was calculated with the Modification of Diet in Renal Disease equation. Patients with decreased renal function (estimated GFR on admission <45 ml .min(-1) . 1.73 m(-2)) were re-hospitalized more frequently than were patients with preserved renal function (estimated GFR on admission >or=45). Patients with decreased renal function were older and had higher rates of anemia, worsening renal function during hospitalization, and previous hospitalization for CHF. Independent predictors of re-hospitalization for CHF identified with multivariate analysis were age, previous hospitalization for CHF, decreased renal function, and non-use of an angiotensin-converting enzyme inhibitor or angiotensin-receptor blocker.

CONCLUSIONS

Renal dysfunction is an independent predictor of re-hospitalization for CHF, so careful follow-up is needed, even after discharge.

Add-on therapy with a nighttime dose of doxazosin in patients with uncontrolled hypertension: effects on autonomic modulation of the cardiovascular system

This study was designed to determine whether or not the addition of a single nighttime dose of doxazosin in extended-release form (GITS; gastrointestinal therapeutic system) would affect the autonomic modulation of the cardiovascular system in patients with uncontrolled hypertension treated with a multi-drug regimen. Resting 5-min noninvasive finger blood pressure and ECG signals, as well as 24-h Holter ECGs, were recorded in 30 patients with uncontrolled hypertension on multi-drug treatment before and after 16-week add-on therapy with doxazosin GITS. Cardiovascular autonomic modulation was evaluated by spectral analysis of heart rate variability (HRV) and a cross-correlation method for spontaneous baroreflex sensitivity (BRS) in 5-min resting recordings, and by the analysis of Poincaré plots and phase-rectified signal averaging of the duration of cardiac cycles in 24-h ECG recordings. This combined therapy significantly reduced systolic pressure (19.4+/-3.5 mmHg; p<0.0001), diastolic blood pressure (9.4+/-2.0 mmHg; p=0.0003), and pulse pressure (10.0+/-2.8 mmHg; p=0.0021). Concomitantly, there was a significant increase in resting spontaneous BRS (p=0.0191) and increases in 24-h short-term (p=0.0129) and total (p=0.0153) HRV, but with no significant change in heart rate or other measures of HRV. The improvements in HRV and BRS were observed mainly in patients already treated with thiazide diuretics. There was a significant association (r=0.49; p=0.0065) between the degree of change in diastolic blood pressure and short-term HRV caused by the combined treatment. The addition of 4 mg doxazosin GITS to multi-drug antihypertensive therapy is associated with an improvement in cardiovascular autonomic control.

Catecholamines regulate the activity, secretion, and synthesis of renalase

BACKGROUND

We previously identified renalase, a secreted novel amine oxidase that specifically degrades circulating catecholamines. Parenteral administration of either native or recombinant renalase lowers blood pressure, heart rate, and cardiac contractility by metabolizing circulating catecholamines. Renalase plasma levels are markedly reduced in patients with chronic kidney disease. It is not known whether endogenous renalase contributes to the regulation of catecholamines.

METHODS AND RESULTS

We show here that circulating renalase lacks significant amine oxidase activity under basal conditions (prorenalase) but that a brief surge of epinephrine lasting <2 minutes causes renalase activity to increase from 48+/-18 to 2246+/-98 arbitrary units (n=3; P<0.002). Enzyme activation is detectable within 30 seconds and sustained for at least 60 minutes. Analysis of epinephrine-mediated hemodynamic changes in normotensive rats indicates that prorenalase becomes maximally activated when systolic pressure increases by >5 mm Hg. The catecholamine surge also leads to a 2.8-fold increase in plasma renalase concentration. Cultured cells exposed to dopamine upregulate steady-state renalase gene expression by >10-fold. The time course of prorenalase activation is abnormal in rats with chronic kidney disease.

CONCLUSIONS

These data identify a novel mechanism for the regulation of circulating catecholamines. In the renalase pathway, excess catecholamine facilitates the conversion of prorenalase, an inactive plasma amine oxidase, to renalase, which can degrade catecholamines. Excess catecholamines not only regulate the activation of prorenalase but also promote its secretion and synthesis. Because chronic kidney disease is associated with a number of systemic abnormalities, including activation of the sympathetic nervous system, increased catecholamines levels, cardiac hypertrophy, and hypertension, renalase replacement is an attractive therapeutic modality owing to its role in catecholamine metabolism.

Leg sympathetic response to noxious skin stimuli is similar in high and low level human spinal cord injury

OBJECTIVE

To determine if sympathetically mediated vasoconstriction in the lower extremities is injury level dependent. Although sympathetic responses have been measured in the limbs of people with high and low level SCI using blood flow measurements, including Doppler ultrasound and venous plethysmography, a direct comparison between injury levels has not been made.

METHODS

Volunteers with chronic SCI were grouped according to injury level. Above T6: high level (HL, n=7), and T6 and below: low level (LL, n=6). All subjects had complete motor and sensory loss. Leg arterial flows were recorded by venous occlusion plethysmography, and continuous heart rate and mean arterial pressure (MAP) were measured. The conditioning stimulus consisted of transcutaneous stimulation to the arch of the contralateral foot.

RESULTS

HL and LL subjects demonstrated a significant decrease in arterial conductance during stimulation with no significant difference found between groups. As expected, only group HL demonstrated a significant increase in MAP.

CONCLUSIONS

These results support our hypothesis that local (leg) sympathetic responses are similar for both high and low level SCI.

SIGNIFICANCE

While low level SCI does not typically present with autonomic dysreflexia, bouts of increased reflex sympathetic activity could have ramifications for metabolism as well as renal and motor system function.

High plasma norepinephrine levels associated with beta2-adrenoceptor polymorphisms predict future renal damage in nonobese normotensive individuals

Renal injury is common in obesity and hypertension. In the present study, we examined relationships between renal function alterations, plasma norepinephrine (NE), and beta2-adrenoceptor polymorphisms in a longitudinal design over 5 years. In 219 nonobese, normotensive men with entry-normal renal function, we measured serum blood urea nitrogen (BUN), creatinine, creatinine clearance, plasma NE, homeostasis model assessment of insulin resistance (HOMA-IR), body mass index (BMI), total body fat mass, and blood pressure (BP) annually for 5 years. beta2 (Arg16Gly, Gln27Glu)-adrenoceptor polymorphisms were determined. The subjects were stable in body weight and BP (<10%) for 5 years. High plasma NE was defined as > or =mean+1 SD at entry. Thirty-seven subjects had entry-high plasma NE and 182 were entry-normal. Entry-high plasma NE subjects had significantly greater total body fat mass and plasma NE and significantly lower creatinine clearance at entry and throughout the study. Increases in BMI, fat mass, BP, plasma NE, BUN, and creatinine, as well as the reduction in creatinine clearance in the 5 years, were significantly greater in entry-high NE subjects. These subjects had significantly higher frequencies of the Gly16 allele of beta2-adrenoceptor polymorphisms. Throughout the study, subjects carrying the Gly16 allele had higher plasma NE, HOMA-IR, and fat mass, and significantly greater reductions in creatinine clearance. Plasma NE at entry was a determinant variable for changes in BUN, creatinine, and creatinine clearance over the 5-year period in multiple regression analysis. In conclusion, high plasma NE at entry, associated with the Gly16 allele of the beta2-adrenoceptor polymorphisms, predict renal function deterioration (seen in elevations of BUN and creatinine and reduction of creatinine clearance) over a 5-year period accompanying further heightened sympathetic nerve activity and deterioration of insulin resistance.

Identification, expression and tissue distribution of a renalase homologue from mouse

FAD (flavin adenine dinucleotide)-dependent monoamine oxidases play very important roles in many biological processes. A novel monoamine oxidase, named renalase, has been identified in human kidney recently and is found to be markedly reduced in patients with end-stage renal disease (ESRD). Here, we reported the identification of a renalase homologue from mouse, termed mMAO-C (mouse monoamine oxidase-C) after the monoamine oxidase-A and -B (MAO-A and -B). This gene locates on the mouse chromosome 19C1 and its coding region spans 7 exons. The deuced amino acid sequences were predicted to contain a typical secretive signal peptide and a conserved amine oxidase domain. Phylogenetic analysis and multiple sequences alignment indicated that mMAO-C-like sequences exist in all examined species and share significant similarities. This gene has been submitted to the NCBI GenBank database (Accession number: DQ788834). With expression vectors generated from the cloned mMAO-C gene, exogenous protein was effectively expressed in both prokaryotic and eukaryotic cells. Recombinant mMAO-C protein was secreted out of human cell lines, indicating the biological function of its signal peptide. Moreover, tissue expression pattern analysis revealed that mMAO-C gene is predominantly expressed in the mouse kidney and testicle, which implies that kidney and testicle are the main sources of renalase secretion. Shortly, this study provides an insight into understanding the physiological and biological functions of mMAO-C and its homologues in endocrine.

Are differences in calcium antagonists relevant across all stages of nephropathy or only proteinuric nephropathy?

PURPOSE OF REVIEW

The main effects of classic calcium antagonists are mediated by the inhibition of L-type calcium channels broadly distributed within the renal vascular bed. Calcium antagonists act predominantly on the afferent arterioles, and dihydropyridines can favour the increase in glomerular hypertension and progression of kidney diseases, in particular when systemic blood pressure remains uncontrolled.

RECENT FINDINGS

Calcium antagonists have been widely used in clinical practice because of their antihypertensive capacity. The prevention of renal damage is a very important aim of antihypertensive therapy. This is particularly so taking into account the high prevalence of chronic kidney disease in the general population. Non-dihydropyridines such as verapamil have been shown to possess an antiproteinuric effect that could be particularly relevant.

SUMMARY

Recent data from clinical trials have confirmed that, in hypertensive patients with preserved renal function or with chronic kidney disease, calcium antagonists are effective antihypertensive drugs to be considered alone or in combination with an angiotensin-converting enzyme inhibitor or an angiotensin receptor blocker. In those patients presenting with proteinuric kidney disease, non-dihydropyridines could reduce proteinuria to a greater degree than dihydropyridines.

Influence of cisplatin-induced renal failure on the α1-adrenoceptor subtype causing vasoconstriction in the kidney of the rat

This study investigated whether the alpha(1)-adrenoceptor subtype(s) mediating the vasoconstrictor actions of the renal sympathetic nerves were altered in rats with cisplatin-induced renal failure. Male Wistar Kyoto rats were used and half received cisplatin (5 mg/kg i.p.) to induce renal failure and were taken for study 7 days later. The renal blood flow reductions caused by electrical renal nerve stimulation and close intra-renal administration of noradrenaline, phenylephrine and methoxamine were determined before and after amlodopine (AMP), 5-methylurapidil (MeU), chloroethylclonidine (CEC) or BMY 7378. Water intake and creatinine clearance were decreased (P<0.05) by 40-50% while fractional excretion of sodium was increased two-fold in the cisplatin treated rats. Mean arterial pressure was higher, 110+/-2 versus 102+/-3 mmHg and renal blood flow was lower, 10.7+/-0.9 versus 18.9+/-0.1 ml/min/kg in the renal failure rats (both P<0.05). AMP, MeU and BMY 7378 decreased (all P<0.05) the adrenergically induced renal vasoconstrictor responses in the renal failure groups by 30 to 50% and in normal rats by 20 to 40%. In the presence of CEC, renal nerve stimulation and noradrenaline and methoxamine induced renal vasoconstrictor responses were enhanced (all P<0.05) in the renal failure but not in the normal rats. These data showed that alpha(1A)- and alpha(1D)-adrenoceptors were the major subtypes in mediating adrenergically induced renal vasoconstriction but there was no substantial shift in subtype in renal failure. The contribution of alpha(1B)-adrenoceptor subtypes either pre- or post-synaptic appeared to be raised in the renal failure rats.

Renalase, a new renal hormone: its role in health and disease

PURPOSE OF REVIEW

Renalase is a secreted amine oxidase that metabolizes catecholamines. The approach used to identify this novel renal hormone will be discussed, as will the experimental data suggesting it regulates cardiovascular function, and its deficiency contributes to heightened cardiovascular risks in patients with chronic kidney disease.

RECENT FINDINGS

The sympathetic nervous system is activated in chronic kidney disease and end-stage renal disease, and patients have a significant increase in cardiovascular disease. Parenteral administration of either native or recombinant renalase lowers blood pressure and heart rate by metabolizing circulating catecholamines. Plasma levels are markedly reduced in patients with chronic kidney disease and end-stage renal disease. Renalase deficiency occurs in salt-sensitive Dahl rats as they develop hypertension. Renalase inhibition by antisense RNA increases baseline blood pressure, and leads to an exaggerated blood pressure response to adrenergic stress. Most recently, two single nucleotide polymorphisms in the renalase gene were found to be associated with essential hypertension in humans.

SUMMARY

The renalase pathway is a previously unrecognized mechanism for regulating circulating catecholamines, and, therefore, cardiac function, and blood pressure. Abnormalities in the renalase pathway are evident in animal models of chronic kidney disease and hypertension. Collectively, these data suggest that renalase replacement may be an important therapeutic modality.